#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
#define rep(i, a, b) for (int i = (a); i <= (b); i++)
#define per(i, a, b) for (int i = (a); i >= (b); i--)
#define endl '\n'
const int N = 2e5 + 5;

int n, m;

int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  cin >> n;
  priority_queue<int, vector<int>, greater<int>> pq;
  vector<int> a;
  int ans = 0;
  rep(i, 1, n * 2) {
    string op;
    int x;
    cin >> op;
    if (op == "add") {
      cin >> x;
      a.push_back(x);
      pq.push(x);
    } else {
      if (a.size()) {
        if (a.back() != pq.top())
          ans++, a.clear();
        else
          a.pop_back();
      }
      pq.pop();
    }
  }
  cout << ans;
  return 0;
}